1. Field of the Invention
This invention relates to downhole well tools, and in particular, to a mule shoe having a surface adapted to cam the mule shoe in only one predetermined angular direction.
2. Description of the Prior Art
It is known in the art of orienting tools and other related downhole well apparatus to utilize a device known as a mule shoe to align or orient a member being lowered into a well bore with respect to a key member extending radially inwardly with respect to the bore casing. For example, U.S. Pat. Nos. 2,207,505 (Bremner), 2,246,417 (Smith), 1,851,319 (McCoy), 3,718,194 (Hering), 3,363,703 (Shewmake), 3,052,309 (Eastman), disclose mule shoe devices. In addition, Sperry-Sun Catalog 767 at page 5198 also discloses a mule shoe apparatus.
In the context of the above-indicated references, that is, in a directional drilling environment, it is necessary to orient a directional finding apparatus lowered into a well bore with respect to a deflecting head or drill bit already downhole. The mule shoe shown in the above-cited references disposes a double-cam face terminating in an axially extending slot. The cam faces wind about the axis of the mule shoe and meet at a point appoximately 180.degree. from the slot.
Depending upon which of the cam surface first engages the key at the lower end of the bore, the mule shoe is subjected to a torquing force in either a right-handed or a left-handed angular direction. It is recognized that the left-hand torque imposed upon the mule shoe assembly acts in a back-off direction, or in a direction tending to un-thread the engagement between the mule shoe and the members threaded thereabove in the string dropped into the bore.
Accordingly, it is advantageous to prevent the imposition of a torquing force on the mule shoe and related assemblies which would tend to back-off the threaded engagement between the constituent parts in the string lowered into the bore.